This type of a grid plate is the subject of U.S. Pat. No. 4,111,585, and is equipped With a bottom and vertical one-piece side walls which are arranged like the walls of a honeycomb, creating hexagonal chambers open toward the top. The bottom of each chamber is provided with a circular drainage hole. Grid plates of this type are used to sow grass by filling the chambers with soil. The grass takes root in the subsoil through the drainage holes.
To sow grass over larger areas, the grid plates are arranged side by side, wherein the rim-bordering side walls of adjacent plates contact one another. To prevent the grid plates from shifting, projections in the form of detents are provided on the plate rim at the bottom which protrude beyond the rim-bordering side walls and engage in detent recesses at the bottom of adjacent grid plates. Along an edge of the plate, detents and recesses alternate. The detents grip into the recesses of the adjacent grid plate from below.
To permit the grass to take root between adjoing chambers, the side walls are provided with slots on the upper part thereof.
These grid plates have a number of disadvantages. Since the peripheral side walls of adjacent plates must lie flush against one another, their proper placement is prevented when stones and soil enter between adjacent side walls. These stones and the soil must be removed as it is otherwise not possible for adjacent grid plates to come to rest against one another. Since the detents and recesses alternate along the plate rim, adjacent plates must be tilted so that the detents of one plate interlock in the recesses of the other plate and vice versa. A further disadvantage is that the slots on the upper part of the side walls are sharp-edged and could, therefore, cause injuries.